One common application for thermal sensors is in thermal (infrared) imaging systems such as night vision equipment. One class of thermal imaging systems includes a focal plane array of thermal sensors or pixels coupled with an integrated circuit substrate. The signals from the pixels are addressed by the integrated circuit substrate and processed to produce a picture of a thermal scene.
Typically, thermal imaging systems undergo testing prior to delivery to calibrate the sensitivity of individual pixels and to identify defective pixels. This pre-delivery testing may include flooding the thermal imaging system with a uniform infrared source, capturing the signals produced by the pixels, and identifying as defective those pixels that respond to the thermal energy with signals outside a target range. The identified defective pixel signals may be substituted with signals of adjacent operative pixels to produce a picture of the thermal scene with minimum distortion. The identity of defective pixels may be programmed into a memory, such as an EPROM, EEPROM, or SRAM, which is supplied to the customer at delivery.
There is a high probability that some pixels will become defective with extended use. Even small percentages of additional, nonsubstituted signals from defective pixels may severely degrade the displayed picture of the thermal scene, as well as the customer's perception of the product. Several approaches have attempted to perform substitution of defective pixel signals, but these systems are complex, costly, and may be incompatible with the space and power limitations of thermal imaging systems in a tactical environment.